A Daily Walk Can Reduce the Power of Weight-Gaining Genes

Body weight, like so many of our individual characteristics, is the combined result of the genes we’re born with and the way we live our lives — how much and what we eat, and whether we exercise. The question is, how much does one influence the other?

Qibin Qi of the Harvard School of Public Health and his colleagues say that walking for about an hour a day can reduce the weight-promoting effect of certain genes by 50%. What’s more, the scientists say, sedentary activities like watching TV can trigger the weight-gaining effect of the same genes.

The study involved more than 12,000 men and women enrolled in the long-running Nurses’ Health Study and Health Professionals Follow-Up Study, which track lifestyle behaviors and health outcomes among doctors and nurses and other health care professionals. In order to determine how much influence the weight-gaining genes had on the participants’ weight, Qi and his colleagues focused on 32 genes that have previously been linked to body mass index (BMI), a ratio of height and weight that is used to determine overweight and obesity.

The researchers plotted the participants’ BMI against their so-called weight-gene score, a measure of how many variants of the 32 genes they possessed. Because we obtain one copy each of every gene from our mother and father, the maximum number of weight-promoting variants a subject could have was 64, and the minimum was zero. It turned out that no one was burdened with two copies of every BMI-increasing gene; the maximum number of variants in the study subjects totaled 43, while the minimum number of variants was 10. Based on this comparison, the researchers determined that for every genetic variant, the effect on BMI was to increase it by 0.13 kg/m2.

But among those who walked briskly for about an hour a day, this genetic effect was reduced by 50%, to 0.06 kg/m2. It’s the first study to bring the effect of exercise down to the genetic level, and to measure how physical activity can change the way genes work — in this case by inhibiting the activity of genes that promote weight gain.

The study also documented an increase in the activity of these genes among those who were more sedentary. For every two hours spent in front of the television every day, there was a 0.3 kg/m2 increase in BMI.

The fact that walking and TV watching each had independent effects on BMI hints that it’s important both to increase exercise and reduce sedentary time in order to lose weight. In other words, it’s not enough to be physically active most of the day if you’re still sitting on the couch watching TV for several hours. “We suggest that both increasing physical activity and reducing sedentary behavior can lower the genetic predisposition to obesity,” says Qi.

The authors acknowledge that it may not be the act of TV watching itself that enhances the activity of the weight-promoting genes. It may be that people who watch more TV also tend to eat more and exercise less, for example. But the latest findings provide some hope that even if you’re not blessed with lean genes — and not many of us are — you can modify the fattening effect of your DNA by changing how you live your life.

A History of Kids and Sleep: Why They Never Get Enough

For many a frazzled parent, bedtime — their children’s, that is — is the best part of the day. But it can be hard to ease snooze-averse kids into bed, and now a new study confirms that this is an age-old problem: children have consistently gotten less sleep than recommended guidelines, for at least the past 100 years.

Researchers from the University of South Australia did some historical spelunking, looking for every study about sleep duration in children beginning from the end of the 19th century through 2009. They discovered 300 such studies, dating all the way back to a French paper from 1897, and found that both age-specific recommendations for appropriate sleep and the amount of time kids actually spend in dreamland both declined at similar rates: 0.71 minutes per year for recommendations versus o.73 minutes per year for actual sleep duration, according to the study published Monday in the journal Pediatrics. Across the board, children got about 37 minutes less sleep than was recommended.

Another constant: societal hand-wringing over children’s lack of sleep and a tendency to blame the hectic pace of modern life.

“We found that indeed kids are sleeping less,” says senior author Tim Olds, a professor of health sciences at the University of South Australia in Adelaide, who studies health and how we use our time. “People are always recommending kids sleep more than they do.”

Over the 112 years the study covered, children lost about 75 minutes of shut-eye: in 1897, experts were recommending that kids sleep 1 hr. 15 min. more than was advised in 2009.

What’s perhaps most eye-opening is the researchers’ observation that sleep recommendations are pretty subjective; there’s just not that much empirical evidence about how much sleep children actually need.

So, how much are kids supposed to sleep anyway? The National Sleep Foundation in Arlington, Va., says babies between the ages of 3 to 11 months should snooze for a total of 14 to 15 hours, while toddlers between 1 to 3 years old should get 12 to 14 hours. Preschoolers need 11 to 13 hours, and elementary schoolers should sleep between 10 to 11 hours. Older children and teens need a minimum of 8½ hours.

Assessing sleep needs is complicated because tracking how long a child sleeps doesn’t tell you how long he should be sleeping; he may not be getting enough z’s or he may be getting too many. Other research has found that 20% of kids report they’re sleepy during the day and can’t focus in school; 60% say they’d like to get more sleep. So perhaps they do need more sleep. But in reality, there is almost no evidence about how much sleep kids truly need to function their best. “We think for no particularly good reason that kids need more sleep than they’re getting,” says Olds. “Every so often a group of blokes get together and say, What do you recommend, boys? Should we push it up to 9 hours, 15 minutes? It really is like that, honestly. It’s an arbitrary public-health line in the sand that people draw.”

Throughout the study period, concerns were expressed that modern life and overstimulation prevented children from getting the sleep they need. As far back as the late 19th century, an editorial in the British Medical Journal bemoaned our sleepless society, the stress and bustle of everyday life, the gaslights and the trolley cars. In 1905, one study noted that “this is a sleepless age and more and more … we are turning night into day.” Says Olds: “Throughout the 100-year period, we have been blaming whatever the new technology is — radio, TV, the Internet. Information is coming in so fast that we never wind down.”

What’s more, different countries have different standards: in Japan, for example, it’s more or less accepted that kids doze off in class because they’ve stayed up late studying. Australian kids sleep almost an hour more a day than American kids, who sleep less than nearly all other children.

“We’re not saying kids don’t need more sleep,” says Olds. “My hunch is yes, they do need more sleep, but we haven’t seen good evidence of that.”

The take-home message, according to Olds? “Never trust sleep experts.”